Pickling solution



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Patented Sept. 25, 1934 UNITED STATES I PICKLING SOLUTION i" f" George C. Kiefer, Springdale, Pa., assignor to Allegheny Steel Company, Brackenridge, Pa., a

corporation of Pennsylvania No Drawing. Application January 28, 1930, Serial No. 424,142

13 Claims.

This invention relates to pickling solutions, and has especial reference to such solutions for use in the pickling of chromium-containing alloy steels as for example, chrome steels and chro- 5 mium-nickel steel alloys.

An object of the invention is to provide a pickling solution which will remove scales from chromium-containing alloy steels as for example, chrome steels and chromium-nickel alloy steels,

without corroding or pitting the metallic surface of the alloy, and which will effectively clean the metal within a permissible period of time.

The scale which forms on the chromium-containing alloy steels as for example, chrome steels 5 and chromium-nickel alloy steels adheres closely to the surface of the metal, and even after the regular annealing process, considerable difficulty is encountered in removing the same in reasonable periods of time without damaging the surface of the alloy. The pickling solutions in general use either do not remove all of the scale, or if exceptionally strong solutions are used, the aloy surface is frequently corroded and pitted.

I have found that suitably annealed chromium- 5 containing alloy steels as for example, chrome steels and chromium-nickel alloy steels, and especially such alloys which contain from ten to thirty percent of chromium, and from five to twenty-five percent of nickel, with or without additions such as tungsten, molybdenum, copper, etc. etc., and which acquire highly refractory scales, may, after proper annealing, be successfully pickled in a solution containing from five I claim:

1. For use with annealed 18% chromium 8% nickel alloy steel having a difiicultly removable, closely adherent, highly refractory scale, a heated pickling solution containing by volume about of commercial nitric acid and about 2% of hydrofluoric acid (48%), which will not attack the alloy surface.

2. A pickling solution of mixed character adapted for removing scale of highly refractory, closely adherent nature, such as that acquired by chromium-containing alloy steels, e. g., chrome steels and chro -nickel steels, and comprising about 20-25 0 y volume of commercial nitric acid intermixed with about 1-3% of hydrofluoric acid (48%) by volume, the composite pickling solution effectively removing such scale and the cleaned alloy surface being unattacked thereby.

3. A pickling solution of mixed character adapted for removing highly refractory, closely 75 adherent scales such as those acquired by chrome and chrome-nickel steels, particularly after annealing thereof, comprising commercial nitric acid to an amount over 5% and up to 25% by volume and an appreciable amount of hydros0 fluoric acid (48%) up to about but less than 4% by volume.

4. The method of treating alloys of chromium and iron to remove surface stains and scale, comprising immersing the alloy in an aqueous bath 85 containing nitric acid and hydrofluoric acid, the amount of nitric acid being greater than any other acid.

percent to twenty-five percent of commercial 5. The method of treating alloys of chromium ant ens, and fip'fo' five percent of commercial (45%) hydronuWr-trle percentages used being by' volume. The composition of a particular solution may be selected for a special case. Desirable solutions contain from twenty percent to twenty-five percent of commercial nitric acid,

and from one percent to three percent of hydrofluoric acid (48%), by volume. With an annealed alloy steel containing about eighteen percent of chromium, and about eight percent of nickel, a

preferred pickling solution would contain about mnty -five percent by volume of commercial itric acid, and about twqpercent by volume of and'iron to remove surface stains and scale, comprising immersing the alloy in an aqueous bath containing nitric acid as its predominant active constituent, and also containing from .05 to 5% hydrofluoric acid.

6. The method of treating alloys of chromium and iron to remove surface stains and scale, comprising immersing the alloy in an aqueous bath containing from 3 to 25% nitric acid and from .05 to 5.0% of hydrofluoric acid, the amount of nitric acid being greater than any other acid.

7. The method of treating alloys of chromium and iron to remove surface stains and scale, comh rofiuoric acid, (48%)," pr'eferably heated, prising immersing the alloy in an aqueous bath S fihaTn'ixedsolution has been found tube 50 highly effective in removing scale from this class of alloy steels, and does not corrode the exposed surface of the alloy.

Exhausted pickling solutions may be treated chemically or' electrochemically for the recovery 55 of their .values.

containing from 3 to 25% nitric acid and an effective amount of hydrofluoric acid, the amount of nitric acid being greater than any other acid.

8. The method of treating alloys of chromium and iron to remove surface stains and scale, comprising immersing the alloy in an aqueous bath containing from 7 to 25% of nitric acid and an 110 LAGHHHUI 11. An aqueous pickling bath for chromiumiron alloys containing from 3 to 25% nitric acid and from .05 to 5.0% hydrofluoric acid the amount of nitric acid being greater than any other acid.

12. An aqueous pickling bath for chromiumiron alloys containing from 7 to 25% nitric acid and from .5 to 1.0% hydrofluoric acid.

13. An aqueous pickling bath for chromiumi'ron alloys containing about 25% nitric acid and about 1% hydrofluoric acid.

GEORGE C. KIEFER.

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